Dental articulators are a common and necessary apparatus in the fabrication of a dental prosthesis. Stripped to its bare essentials, the process of fabricating a prosthesis commences when the dentist takes impressions of the patient's maxillary and mandibular arches which may or may not include natural teeth. These impressions are negative imprints of the arches and become the molds into which the raw material for forming positive dental casts is poured. These positive casts are duplicates of the patient's arches (with or without teeth) and become the primary model to which the prosthesis is to be constructed.
In order to construct an acceptable prosthesis, these dental casts are normally mounted in a dental articulator in order that the maxillary and mandibular casts are maintained in the same anatomical relationship as in the mouth of the patient. This is true in all cases, even those where only one prosthesis, as for example, the maxillary arch is to be constructed; since the prosthesis must also conform with the relating surfaces on the mandibular arch in the patient's mouth.
Another reason why the dental casts are mounted in the articulator is to permit arrangement of the denture (false) teeth in their proper position for occlusion. On partial dentures, the occlusion of the denture teeth must be with natural teeth. On full dentures greater liberty is often taken to improve function and asthetics. The desired occlusion not only includes the vertical bite, but also a degree of lateral movement as well as posterior and anterior movement of the lower jaw. These various movements are produced by the temporomandibular joint which is the joint formed by the condyle of the mandible and the temporal bone. Many dental articulators are built to simulate these movements to a high degree.
Past practice for countless years has been to mount the dental casts in the articulator by means of plaster which is usually a gypsum material. This locates the dental casts in a fixed position. Mounting the dental casts by means of plaster is relatively expensive, is dusty and time consuming because the powdered raw material must be thoroughly mixed with a liquid and the plaster must be allowed to set, the process is subject to error which cannot be compensated, and all utensiles must be thoroughly cleaned after each use. Even in cases where the dental casts have been provided with grooves to facilitate removal and remounting which is usually a requirement in the fabricating process, it is very questionable, at best, whether or not the casts are remounted to their precise originally mounted positions.
At least 95% of all dental articulators built to date have been built for use with the plaster mounting techniques. A few have been built which use mechanical mounting devices such as claws or other clamping devices in an attempt to find a better mounting technique than by the use of plaster. These alternate mounting techniques have been far less satisfactory than plaster, especially in those situations where the dental casts are to be removed and remounted to their original positions.
The principal cause for the difficulty was that the casts were retained in a manner which did not have firmly established locating positions; therefore, the casts could not be remounted to their precise original positions in the articulator. The first known articulator in which the casts could be remounted to their precise original position by means other than the plaster mounting articulators is the articulator taught in the referenced application Ser. No. 788,236 in which this was accomplished by means of threaded apertures in the base of the casts; one method for forming the threaded apertures being taught in the referenced U.S. Pat. No. 3,975,489. The articulator taught in referenced U.S. Pat. No. 4,169,314 also uses a threaded aperture in the base of the casts.
As will be shown, the new apparatus and mounting techniques of the present invention introduce an entirely new concept for the mounting of dental casts.